Electric heating apparatus



April 1929- A. s. MACDONALD ET AL 1,708,512

ELECTRIC HEATING APPARATUS Filed Aug. 28, 1925 2 Sheets-Sheet 1 P 1929. A. s.- MACDONALD ET AL 1,708,512

ELECTRIC HEATING APPARATUS Filed Aug. 28, 1923 2 SheecS-Sheet 2 Patented Apr. 9, 1929.

UNITED STATES PATENT OFFICE.

' ANGUS S. MACDONALD, OF GREAT NECK, NEW YORK, AND CHARLES C. WAITE, OF ROSELLE PARK, NEW JERSEY, AND EDWARD MELVILLE HUGGINS, OF NEW YORK, N. Y., ASSIGNOBS TO SNEAD & COMPANY, CF JERSEY CITY, NEW JERSEY, A GOR- I'OBATION OF NEW JERSEY.

ELECTRIC HEATING APPARATUS.-

Application filed August 2a, 1923. Serial No. 659,743.

, Our invention relates to electrical heating apparatus and methods, and is advantageous for the heating and heat treatment of small objects and pieces,-sucli as short rods (1n- 5 eluding hollow rods, or tubes), blocks, discs, washers, nuts, etc., by passage of electrlc cur rent through the objects. The invention lends itself especially to the simultaneous treatment of numerous pieces of such character as discs, washers, nut-s, etc., and enables such articles, when of like area, to be treated conveniently, expeditiously, economically and uniformly.

In carrying out our invention, the ob ect under treatment-Whether a single piece or a temporary stack of pieces-may be held or clamped between terminals employed for the passage of the heating current to and from it. In the case of objects (or stacks of pieces) offering large contact resistance, considerable endwise pressure may be brought to bear on them between the clamps, and other measures may also be employed to min imize the total resistance from clamp to clamp through the object. For the purpose of holding or exerting pressure on the obJect, the clamps may be yieldingly urged'together, so as to accommodate themselves to thermal variations in the dimensions of the object. The heating operation may be controlled according to the relative movement of the clamps, either automatically, by a switch or rheostat actuated by such movement, or by virtue of an indicating device responsive thereto.

At the proper time, the object under treatment may be quenched in any suitable manne1',-as by discharging the same from the apparatus into a bath, plunging the entire apparatus into a bath, or otherwise applying a quenching agent to the articles in the machine. In the case of hollow objects, provision may be made for passage of the quenching agent to or from their interior through one of the clamps.

For the benefit of those desiring to practice our invention, we have here illustrated and described several forms of apparatus in which the various broad features of operation above described can be combined.

In the drawings, Fig. 1 is a somewhat diagrammatic side view of one such apparatus,

and Fig. 2 a similar view of a somewhat different apparatus.

F ig. 3 is a fragmentary side view illustrating (with considerable exaggeration) means of diminishing contact resistance between adjacent articles.

Fig. 4 is a similar view of a stack of articles to be heated, illustrating the use of adaptive devices for this purpose.

The apparatus shown in Fig. 1 has a yokelike frame structure 10 that carries the'terminals or clamps 11, 12 (as they are commonly termed), and sustalns any pressure exerted by them upon theobject P to be heated. In the present instance, the lower clamp 11 is fixed on the yoke 10, but electrically insulated therefrom, as indicated at 13; while the upper clamp 12 is movable relatlvely to the yoke 10, toward and away from the lower clamp 11. If preferred, the movable clamp 12 may be electrically connected to the yoke 10 in any suitable manner, as by means of a U-shaped laminated flexible'conductor 14. These arrangements (as to mobility and insulation of the clamps) can, of course, be varied considerably. Electric current may be supplied from any suitable source, such as a transformer 15 with its secondary connected across the clamps 11, 12, and with its primary variable (as indicated at 1(5) to regulate the current according to requirements. a

To hold the object P and exert any desired endwise pressure on it, the clamps 11, 12 may be yieldingly urged together by any suitable motor device. As shown, fluid pressure is employed, and there is a pressure chamber or cylinder 17 with a movable wall or piston 18,the latter here shown as attached or fixed to the clamp 12. By means of a three way rotary control valve 19, hydraulic pressure or compressed air, etc., from a pressure line 21 can be admitted to the cylinder 15, to press the clamp 12 down on the object P: or the cylinder 15 can be vented through an exhaust line 22, to relieve the pressure and release the object. A helical compression spring 23 may be provided, to lift the clamp pressure of the clamps on the object P when the fluid pressure is on. This pressure can, of course, be controlled and regulated exactly as desired by varying the pressure of the fluid supply or its application to the piston 18.

In practice, the object P naturally expands and contracts -with temperature changes.

Not only does the movable clamp 12 yield to accommodate such variations of the object P, but such thermal variations do not at all atfeet the pressure exerted on the object by the clamps. However, the relative movement of the clamps 11, 12 due to temperature changes in the object P may advantageously be utilized as a means of gauging and controlling the heating operation. As shown, the piston 18 has a rod or stem that extends out through the top wall or head of the cylinder 17 to a pin and slot connection 26 with an indicator arm or pointer 27 fulcrumed on a I lug 28 on the cylinder head. The pointer 27 cooperates with a scale 29 mounted on the yoke 10, and thus responds to and affords a visible indication of the movement of the clamp 12 and of the expansion of the piece P. In the present instance, no automatic-switch for the heating current is illustrated; the vigilance of the operator is depended on to make effective the gauging and control of the heating current. As shown, the spring 23 is interposed between the upper cylinder head and the arm 27. The rod 25 and the piston 18 serve to guide the movementof the clamp 12 and keep it in proper alignment.

The manner of operating the apparatus will necessarily depend a good deal on the character of the objects or articles under treatment, as well as on the exact effect that it is desired to produce on such articles. The progress of heating, cooling, and the cr1t1cal points (of recalescence, etc.) are indicated by the movement and the pauses of the pointer 27. Where the object P consists of a stack of case-hardenedsteel rings p such as shown in thedrawings, a high temperature prior to annealing is required by the soft low-carbon steel core, while the case of high-carbon steel requires a lower quenching temperature. Such articles may be heated up to the higher ten'iperatures and then air quenched (in place. in the. clamps 11, 12, with the current shut off) until the temperature has dropped several hundred degrees, through the critical regions of bot-h core and case,thus insuring a refined core. Then the current may be turned on again until a temperature high enough for the case is attained; and as soon as the case has passed its critical region, the article may be quenched with oil (with the current shut off) and thus brought down to an ordinary temperature. The oil or the like for applied in a variet tioned. As here sii quenching may be of ways, as already menown, both the clamps 11 and 12 are hollow, to afford passage for in gress and egress of the quenching agent to and from the interior of the stack of pieces 2, to chill them from the inside. In the present instance, the stream of quenching agent is supplied via the upper clamp 12, through a somewhat/flexible pipe 33 with a rotary two-way control and regulating valve 34; passes down through the stack P; and discharges via the lower clamp 11, through a hole 35 that opens through the bottom of the lower yoke member.

In the apparatus shown in Fig. 2, the yoke- ]ike frame 10 itself forms the secondary of the transformer 15. As shown, the upright leg of the conductive yoke 10 extends through the interior of the laminated core 36, beside the coils of the primary 37,whosc leads are indicated at 38, 38. Accordingly, the lower clamp 11 is not insulated from the yoke 10, but is in effect part of its lower member.

In Fig. 2. various parts and features are marked with the same reference characters as in Fig. 1, as a means of dispensing with merely repetitive description.

In some cases, when the surfaces of the pieces are highly finished, the total resistance from clamp to clamp may be satisfactorily low, even with no more pressure on the clamps than just enough to hold the pieces securely; in other cases, it may be found desirable to impose considerably greater pres sure, so as to reduce the contact resistance from piece to piece. In still other cases (especially if the abutting faces of the pieces p are rather rough or irregular), it may be found desirable to employ some suitable medium as an aid to reducing the contact resistance. In such cases, the irregularity may be compensated, and the effective Contact augmented and improved, by a multitude of conductive particles spread over the contact area, or by a conductive film of like extent.

A film of finely divided or powdered graphite between the parts ;0 is very advantageous. For, first, graphite has a negative pressure resistance coefficient; and second, it has also a negative temperature resistance coeflicient: so that the resistance at a graphited contact decreases both with increasing pressure of the clamps and with rising temperature of the stack P. Such a graphitic contact film is indicated in Fig. 3 with greatly exaggerated thickness: actually, its thickness may be quite imperceptible to ordinary observation,so that Figs. 1 and 2 represent equally well stacks with or without graphitized contacts. In practice, a convenient method of using the graphite is to coat the contact faces of the pieces p with the powdered graphite, as by brushing it on them.

Fig. 4 indicates a somewhat similar method of reducing contact resistance in a stack of pieces p uite rough, irregular, or the like at their a utting aces: i. e., the interposialready described: e.

tion of" soft metal adapters 40 between the pieces. Under the pressure of the clamps, such adapters will conform closely to the Surfaces of the pieces If desired, of course, they may be supplemented with graphite, as g., graphite may be brushed on the faces of both adapters 40 and pieces p. In any case, the adapters 40 compensate for irregularities in the faces of the pieces p, and not only reduce resistance, but also make the stack more stable under the pressure of the clamps 11, 12.

What we claim is:

1. Apparatus for heating objects by passage of current therethrough comprising opposed terminal clamps for holding an object between them, and a fluid pressure chamber with movable wall for yieldingly urging one of said clamps toward the other upon such object, together with means for indicating the heat, and actuating connection thereto from said 'movable wall extending out through the opposite wall of the chamber.

2. Apparatus for heat treating hollow objects with current passed therethrough comprising opposed terminal clamps for holding the objects between them, one of said clamps affording passage to the interior of the object; fluid pressure means for yieldingly urging one of the clamps toward the other upon the object, to exert thereon a pressure unaffected by its thermal expansion or contraction; and means for supplying a quenching agent to chill the object internally; together with expansion indicating means actuated by the clamp movement due to thermal variation of the object.

3. Apparatus for heating objects by pas sage of current therethrough comprising oposedterminal clamps for holding an object tween them; fluid pressure means for yieldingly urging the clamps together upon the object, to exert thereon a pressure unaffected by its thermal expansion or contraction; a transformer for the heating current, with a conductive yoke for sustaining the pressure of the clamps on the object also forming the transformer secondary"; expansion-indicating means actuated by relative movement of the clamps due to thermal variation of the object.

4. Apparatus for heat treating hollow ob jects with current passed therethrough comprising opposed terminal clamps for holding the object between them, one of said clamps affording passage to the interior of the object; fluid pressure means for yieldingly urging the clamps together upon the object; means for supplying a quenching agent to chill the object internally; a transformer for the heating current, with aframe structure carrying the terminals and serving as the transformer secondary; together with means for indicating the heating actuated by relative movement of the clamps due to thermal variation of the object.

5. Apparatus for heat treating hollow objects with current passed therethrough comprising opposed terminal clamps for holding the object between them, and means for supplying a quenching agent to the interior of the object with passage therefor through one of the clamps.

6. Apparatus for heat treating hollow objects with current passed therethrough comprising opposed hollow terminal clamps for holding the object between them, and means for passing heating current from one clamp through the object to the other clamp, and means for passing a quenching agent through the interior of the object via" the hollow clamps.

In testimony whereof, we have hereunto signed our names.

Aueus s. MACDONALD. CHARLES o. WAITE. E. MELVILLE HUGGINS. 

